JP2004277266A - Method for manufacturing compound semiconductor single crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a compound semiconductor single crystal, which is effective for enhancing the speed of crystal growth and for obtaining a long size crystal in VB and VGF methods. <P>SOLUTION: The growth speed and the yield of the single crystal can be enhanced by, after melting a polycrystal raw material and completing seeding, growing the single crystal up to a time point of a cross sectional area increasing part 3b from the seed crystal part 3a subjected to seeding or up to a time point of not longer than 1/4 of the total length in the longitudinal direction of growing crystal part 3c from the seed crystal part 3a subjected to seeding by lowering the temperature at the inside of a furnace (VGF method), then stopping the lowering of the temperature of the furnace, and relatively moving a growth vessel 3 to the growth furnace (VGF method). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a compound semiconductor by a vertical Bridgman method (VB method) and a vertical temperature gradient solidification method (VGF method) in which a raw material melt is gradually solidified from below in a crystal growth vessel to grow a single crystal. The present invention relates to a method for producing a crystal.
[0002]
[Prior art]
As a method for obtaining a compound semiconductor single crystal (GaAs, InP, etc.) having a large diameter exceeding φ3 inches and a low dislocation density, a vertical Bridgman method (LEC method) is used instead of the liquid-sealed Czochralski method (LEC method). The VB method) and the vertical temperature gradient solidification method (VGF method) have attracted attention. The VB method and the VGF method are vertical growth methods in a container in which a single crystal is grown by gradually solidifying a raw material melt from a lower portion to an upper portion in a container. In the LEC method, if growth is performed under a low temperature gradient, dissociation of the group V of a III-V compound semiconductor and dissociation of the group VI of a II-VI compound semiconductor from the crystal after passing through the liquid sealant becomes a problem. , VB method and VGF method are growths in a vertical container, so that dissociation can be prevented by covering the upper part of the container with a liquid sealant. Therefore, since the VB method and the VGF method can grow under a lower temperature gradient than the LEC method, a compound semiconductor single crystal having a low dislocation density can be manufactured.
[0003]
In both the vertical Bridgman method (VB method) and the vertical temperature gradient solidification method (VGF method), a semiconductor raw material melt is housed in a container (crucible), and crystal growth is started from a seed crystal previously arranged at the bottom of the container. This is common in that the crystallization is advanced by gradually solidifying it upward, and finally the entire raw material melt is crystallized. However, the VB method is a method in which the growth is performed by lowering the growth container relatively to the position of the heater, and the VGF method is a method in which the growth is performed only by the temperature drop.
[0004]
In the VB method and the VGF method, the seed crystal mounting portion (seed crystal portion) is located at the lowermost portion, and the diameter increasing portion (cross-sectional area increasing portion) whose diameter increases upward from the seed crystal mounting portion, A growth vessel having a straight body (growing crystal part) extending upward from the part is supported by a support member and arranged in the heating device. Then, the seed crystal is placed in the seed crystal mounting part at the lower part of the growth vessel, and the polycrystalline raw material is placed thereon. Crystallize towards the top.
[0005]
Conventionally, first, in the first half of crystal growth, as in the case of the VB method, in a furnace with a temperature gradient, the vertical container containing the raw material is lowered, and crystals are grown from the lower end of the raw material. There is known a method of growing a compound semiconductor crystal in which the lowering of the container is stopped and the temperature of the furnace is lowered and the crystal is subsequently grown in the same manner as in the VGF method (for example, see Patent Document 1).
[0006]
The method of Patent Document 1 has the following advantages. First, by employing the VB method in the early stage of crystal growth in which the temperature is set to be high, the temperature of the high-temperature portion does not need to be too high. This prevents dissociation of the constituent elements. For this reason, composition deviation is prevented. Next, by employing the VGF method in the middle and late stages of growth, the furnace length can be shortened. In addition, since the VB method is performed first, the temperature gradient is relatively large at the stage of transition from the VB method to the VGF method. Therefore, the growth rate can be easily controlled in the VGF method even in the middle and late stages of growth.
[0007]
[Patent Document 1]
JP-A-4-325485
[Problems to be solved by the invention]
However, in increasing the length of a crystal, it is intended to produce a low-dislocation single crystal at a high yield and at a low cost by making the solid-liquid interface convex or flat on the melt side while increasing the crystal growth rate. From a viewpoint, it has been desired to provide a method of manufacturing a compound semiconductor crystal with further improvement.
[0009]
In order to realize the dislocation reduction which is a feature of the VB method and the VGF method, it is necessary to (i) suppress thermal strain generated after crystal solidification, and (ii) a solid-liquid interface (which shows the crystal solidification shape during crystal growth). ) Has a concave shape (FIG. 4) toward the melt, so that mechanical distortion must be suppressed.
[0010]
Regarding the above point (i), one of the measures against thermal distortion is crystal growth under a low temperature gradient. This is because dislocations caused by thermal distortion during cooling can be suppressed by slowly cooling the crystallized portion and the grown portion under a low temperature gradient.
[0011]
Regarding the above point (ii), when the shape of the solid-liquid interface becomes concave toward the melt, the generated dislocations converge toward the inside of the crystal and polycrystals easily form, so that the VB method and the VGF method use concave growth. In other words, it is essential to suppress dislocations, that is, to make the solid-liquid interface shape convex (FIG. 5) or flat on the melt side.
[0012]
However, for the reasons described above, during the crystal growth by the VB method and the VGF method, since the crystal grows under a low temperature gradient, the amount of heat radiation from the seed crystal part cannot be increased. Therefore, when the crystal growth rate is increased, the amount of heat radiation from the seed crystal portion becomes insufficient, and the solid-liquid interface shape becomes concave toward the melt (FIG. 4). Therefore, when high-speed growth is performed by the VB method and the VGF method, it is very difficult to achieve single crystallization and low dislocation. Also, when the crystal is lengthened, the amount of heat flowing from the raw material melt increases, so the amount of heat radiated from the seed crystal part is insufficient, and the solid-liquid interface shape becomes concave on the melt side. And dislocation reduction are difficult.
[0013]
Therefore, an object of the present invention is to solve the above-mentioned problems and to provide a method of manufacturing a compound semiconductor crystal that is effective for increasing the crystal growth rate and lengthening the crystal by the VB method and the VGF method.
[0014]
[Means for Solving the Problems]
In order to achieve the above object, the present invention is configured as follows.
[0015]
The method of manufacturing a compound semiconductor single crystal according to the first aspect of the present invention is characterized in that a seed crystal portion having a small cross-sectional area, a cross-sectional area increasing portion having a gradually increasing cross-sectional area, and a substantially constant cross-sectional area following the seed crystal portion Using a container having a growing crystal part, the raw material melt is stored in the container, and in a growth furnace provided with a temperature gradient, crystal growth is started from a seed crystal previously arranged at the bottom of the container, and gradually. In the method for producing a compound semiconductor single crystal in which crystallization is advanced upward and finally the entire raw material melt is crystallized, the polycrystalline raw material is melted, and after seeding is completed, the temperature in the furnace is lowered. By growing a single crystal from the seed crystal part after completion of seeding to a certain point of the cross-sectional area increasing part, then, by stopping the decrease in the furnace temperature, the container is moved relatively to the growth furnace. It is characterized by growing a single crystal.
[0016]
The method of manufacturing a compound semiconductor single crystal according to the second aspect of the present invention is a method for manufacturing a compound semiconductor single crystal, wherein a seed crystal portion having a small cross-sectional area, a cross-sectional area increasing portion having a gradually increasing cross-sectional area, and a substantially constant cross-sectional area subsequent thereto are provided. Using a container having a growing crystal part, the raw material melt is stored in the container, and in a growth furnace provided with a temperature gradient, crystal growth is started from a seed crystal previously arranged at the bottom of the container, and gradually. In the method for producing a compound semiconductor single crystal in which crystallization is advanced upward and finally the entire raw material melt is crystallized, the polycrystalline raw material is melted, and after seeding is completed, the temperature in the furnace is lowered. The single crystal is grown from the seed crystal part after completion of the seeding to a point equal to or less than １ ／ of the entire length of the growth crystal part in the longitudinal direction, and then, the temperature in the furnace is stopped from falling, and the container is removed. Single crystal growth by moving relatively to the growth furnace And performing.
[0017]
According to a third aspect of the present invention, in the method for producing a compound semiconductor single crystal according to the first or second aspect, after the polycrystalline raw material is melted and the seeding is completed, the temperature in the furnace is lowered to thereby reduce the seed after the completion of the seeding. The method is characterized in that a single crystal is grown from a crystal part and the average temperature of the raw material melt at the time when the decrease in the furnace temperature is stopped is lower than a temperature higher by 5 ° C. than the melting point.
[0018]
<The gist of the invention>
The gist of the present invention is a method for manufacturing a compound semiconductor single crystal in which the solid-liquid interface is convex or flat to the melt side and the growth rate can be increased or lengthened.
[0019]
That is, a seed crystal portion having a small diameter or cross-sectional area of a circular or arbitrary shape, a growth crystal portion having a large diameter or cross-sectional area of a circular or arbitrary shape and a substantially constant diameter, or a diameter-enlarging portion having a gradually increasing diameter or cross-sectional area. Using a container having a cross-sectional area increasing portion, the raw material melt is stored in the container, and in a growth furnace provided with a temperature gradient, crystal growth is started from a seed crystal previously arranged at the bottom of the container, and gradually. In the compound semiconductor single crystal manufacturing method in which crystallization is advanced upward and finally the entire raw material melt is crystallized, after the polycrystalline raw material is melted and seeding is completed, the diameter is increased or cut from the seed crystal part. After using the method of growing a single crystal by lowering the temperature in the furnace (VGF method) up to a certain point of the area increasing portion, the container is then moved relatively to the growth furnace. Grow single crystal with Performs utilization methods (VB method) which is a compound method for manufacturing a semiconductor single crystal so as to increase the growth rate and yield of the single crystal.
[0020]
In order to completely melt the polycrystalline raw material in a short time and stably seed the polycrystalline raw material in a short time, it is necessary to raise the average temperature in the furnace of the polycrystalline raw material placement part to a certain temperature higher than the melting point. However, after the polycrystalline raw material is completely melted, it does not solidify even if the temperature of the melt is lowered to near the melting point. In the present invention, attention is paid to this point, and the average temperature in the furnace of the polycrystalline raw material placement part is set to be somewhat higher than the melting point (for example, 15 ° C. higher than the melting point) (FIG. 1A), After the raw material is completely melted and stably seeded, the temperature in the furnace is lowered (VGF method), from the seed crystal part after seeding is completed to a point at which the diameter increasing part or the cross-sectional area increasing part is reached or The average temperature of the raw material melt at the time of growing the single crystal from the seed crystal part after completion of seeding to a certain point equal to or less than 1/4 of the entire length of the growth crystal part in the longitudinal direction is reduced to near the melting point (for example, 5 ° C. below the melting point). Lower than the high temperature) (FIG. 1 (b)).
[0021]
By lowering the average temperature of the raw material melt to the vicinity of the melting point with respect to the melting point in this way, the heat flowing from the raw material melt is reduced, and in the subsequent VB method, the solid-liquid interface is flattened and the crystal is cooled. It is possible to increase the growth rate. Further, by increasing the length of the crystal, the inflow heat from the raw material melt at the time of growing the single crystal increases. However, since the inflow heat from the raw material melt can be reduced according to the present invention, long and low dislocations can be obtained. It becomes possible to produce a single crystal.
[0022]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the illustrated examples.
[0023]
In the method for producing a compound semiconductor single crystal of the present invention, the temperature of the raw material melt is reduced to near the melting point while growing the single crystal by lowering the furnace temperature from the seed crystal (VGF method), and then the furnace temperature is reduced. The growth rate and the yield are increased by growing the single crystal by stopping the lowering of the material and moving the raw material container downward (VB method). GaAs, which is one of compound semiconductor single crystals, will be described as an example.
[0024]
1A and 1B show a part of a method for producing a compound semiconductor single crystal of the present invention, in which FIG. 1A is a schematic diagram showing a temperature distribution after melting a raw material and completing seeding, and FIG. After the seeding was completed, the temperature in the furnace was lowered while maintaining the temperature gradient to grow a single crystal from the seed crystal part, and the average temperature of the raw material melt became lower than the temperature 5 ° C. higher than the melting point. It is a schematic diagram showing the temperature distribution at the time of stopping the temperature fall of the furnace temperature.
[0025]
[Example 1]
As shown in FIG. 2, the GaAs single crystal is grown by using a growth furnace which heat-treats with a heating device made of graphite (upper heater 8, middle heater 9, lower heater 10) in an inert gas 2 in a chamber 1. Was done.
[0026]
As a crystal growth container, a seed crystal part 3a formed as a circular seed crystal storage part having a small diameter formed at a lower part, a diameter increasing part (cross-sectional area increasing part 3b) having a diameter gradually increasing upward following the seed crystal part 3a, Then, a PBN crucible 3 having a substantially circular straight body (crystal growth part 3c) having a large circular diameter.
[0027]
A PBN crucible 3 contained GaAs polycrystalline raw material 4, boron trioxide (B ₂ O ₃ ) 5 as a liquid sealant, and seed crystal 6. After that, the crucible 3 made of PBN is set on the crystal receiving table 7 made of graphite. After the setting is completed, the inside of the furnace is evacuated, replaced with an inert gas, and heated by the upper heater 8, the middle heater 9, and the lower heater 10. The upper heater 8 is heated to 1256 ° C., the middle heater 9 is heated to about 1252 ° C., and the lower heater 10 is heated to 1217 ° C. By maintaining the set temperature for 15 hours after the temperature rise, the polycrystalline raw material is completely melted and seeded (see FIG. 1 (a)). The average temperature of the raw material melt after completion of the seeding was about 1254 ° C. (a temperature 16 ° C. higher than the GaAs melting point).
[0028]
By lowering the temperature of the upper heater 8 to 1240 ° C., the temperature of the middle heater 9 to about 1243 ° C., and the temperature of the lower heater 10 to 1208 ° C. (VGF method), a single crystal is grown from the seed crystal part 3 a after the seeding is completed ( FIG. 1 (b). By lowering the temperature (VGF method), the average temperature of the raw material melt is raised at the point of time when a single crystal is grown up to 4/5 of the entire length of the diameter-increasing portion (cross-sectional area increasing portion 3b). It was about 1242 ° C. (4 ° C. higher than the GaAs melting point).
[0029]
Thereafter, the temperature drop in the furnace was stopped, and the crucible 3 made of PBN was moved downward at a speed of 4 mm / hour (VB method) to grow the crystal to the end.
[0030]
By the above method, a low-dislocation GaAs single crystal having a diameter of φ4 inches and a crystal length of 200 mm was obtained.
[0031]
With only the VB method or only the VGF method, it took 170 hours to obtain a GaAs single crystal having a diameter of φ4 inches and a crystal length of 200 mm. However, in the method of the first embodiment, a low dislocation GaAs single crystal can be grown in 150 hours. did it. The solid-liquid interface is convex or flat on the melt side, and the yield is only VB method or VGF method, although the growth rate is increased in the method of Example 1 in comparison with VB method only or VGF method only. It was 70% by the method alone, but was improved to 80% by the method of Example 1.
[0032]
[Example 2]
FIG. 3 shows an outline of the GaAs single crystal growth described here. In the same manner as in Example 1, a PBN crucible 3 was filled with a GaAs polycrystalline raw material 4, boron trioxide (B ₂ O ₃ ) 5 as a liquid sealant, and a seed crystal 6. After that, the crucible 3 made of PBN is set on the crystal receiving table 7 made of graphite. After the setting is completed, the inside of the furnace is evacuated, replaced with an inert gas, and heated by the uppermost heater 11, upper heater 8, middle heater 9, and lower heater 10. The upper heater 11 is heated to 1256 ° C., the upper heater 8 to 1256 ° C., the middle heater 9 to about 1252 ° C., and the lower heater 10 to 1207 ° C. By maintaining the set temperature for 15 hours after the temperature rise, the polycrystalline raw material is completely melted and seeded (see FIG. 1 (a)). The average temperature of the raw material melt after completion of the seeding was about 1254 ° C. (a temperature 16 ° C. higher than the GaAs melting point).
[0033]
By lowering the temperature of the upper heater 11 to 1241 ° C., the upper heater 8 to 1241 ° C., the middle heater 9 to 1243 ° C., and the lower heater 10 to 1198 ° C. (VGF method), from the seed crystal part after completion of seeding A single crystal is grown (see FIG. 1B). When the temperature is lowered (VGF method) and the single crystal is grown until the length of the grown crystal part becomes 30 mm, the average temperature of the raw material melt is about 1242 ° C. (4 ° C. with respect to the melting point of GaAs). High temperature).
[0034]
Thereafter, the temperature drop in the furnace was stopped, and the crucible 3 made of PBN was moved downward at a speed of 3 mm / hour (VB method) to grow the crystal to the end.
[0035]
By this method, a low-dislocation GaAs single crystal having a diameter of φ4 inches and a crystal length of 300 mm was obtained.
[0036]
With only the VB method or the VGF method, it took 270 hours to obtain a GaAs single crystal having a diameter of φ4 inches and a crystal length of 300 mm. However, in the method of Example 2, it was possible to grow a low dislocation GaAs single crystal in 220 hours. did it. The solid-liquid interface is convex or flat on the melt side, and the yield is only VB method or VGF method, although the growth rate is increased in the method of Example 2 in comparison with VB method only or VGF method only. It was 50% by the method alone, but was improved to 70% by the method of Example 2.
[0037]
In the above-described first and second embodiments, single crystal growth of GaAs has been described. However, in addition to GaAs, application to single crystal growth of a compound semiconductor such as InP, GaP or the like is also possible.
[0038]
[Comparative Example 1]
By lowering the temperature in the furnace, a single crystal is grown from the seed crystal part after the seeding is completed, and the average temperature of the raw material melt at the time after the stop of the temperature drop in the furnace is 5 ° C. or more with respect to the melting point. A GaAs single crystal was grown under the same conditions as in Example 1 except that the temperature was higher than 1243 ° C.
[0039]
As a result of performing under the same conditions as in Example 1 except that the average temperature of the raw material melt at the time after the stop of the temperature drop in the furnace was 1243 ° C. or higher, the solid-liquid interface became concave toward the melt and the yield was increased. Was also 70% or less, which was lower than 80% of Example 1.
[0040]
[Comparative Example 2]
By lowering the temperature in the furnace, a single crystal is grown from the seed crystal part after the seeding is completed, and the average temperature of the raw material melt at the time after the stop of the temperature drop in the furnace is 5 ° C. or more with respect to the melting point. A GaAs single crystal was grown under the same conditions as in Example 2 except that the temperature was higher than 1243 ° C.
[0041]
The results were obtained under the same conditions as in Example 2 except that the average temperature of the raw material melt at the time after the stop of the temperature drop in the furnace was 1243 ° C. or higher. As a result, the solid-liquid interface became concave toward the melt and the yield was increased. Was also 60% or less, which was lower than 70% in Example 2.
[0042]
In the case of compound semiconductor single crystal growth of InP, GaP, etc. other than GaAs, when the average temperature of the raw material melt is higher than the melting point by 5 ° C. or more, the solid-liquid interface becomes concave toward the melt. Also, the yield was lower than when the test was performed at 5 ° C. or lower.
[0043]
From the above results, the average temperature of the raw material melt at the time when the single crystal was grown by lowering the temperature while maintaining the temperature gradient from the seed crystal part to the point of the diameter increasing part or the cross-sectional area increasing part By lowering the temperature by 5 ° C. higher than the melting point, the solid-liquid interface becomes convex or flat on the melt side, and a single crystal can be manufactured with a high yield.
[0044]
The growth rate is increased at the time when the single crystal is grown by lowering the temperature while maintaining the temperature gradient from the seed crystal part after completion of seeding to a certain point equal to or less than １ ／ of the entire length of the growth crystal part in the longitudinal direction. The same can be achieved by lowering the average temperature of the raw material melt to around the melting point (for example, lower than a temperature higher by 5 ° C. than the melting point).
[0045]
【The invention's effect】
As described above, according to the present invention, in the manufacturing method of growing a single crystal by the VB method and the VGF method, the temperature is decreased while maintaining the temperature gradient, so that the diameter of the seed crystal part is increased or the sectional area is increased. The average temperature of the raw material melt at the time when the single crystal is grown is reduced to near the melting point until a certain point of the growing part or from a seed crystal part after completion of seeding to a certain point equal to or less than １ ／ of the entire length of the growth crystal part in the longitudinal direction. For example, since the temperature is set to be lower than the temperature which is higher by 5 ° C. than the melting point, the inflow heat from the raw material melt can be reduced.
[0046]
Therefore, by using the method for producing a compound semiconductor crystal of the present invention, the solid-liquid interface can be convex or flat on the melt side when the crystal growth rate is increased and the crystal length is increased, and low dislocation single crystals can be formed. Crystals can be produced. Therefore, a compound semiconductor crystal can be manufactured at a high yield and at a low cost.
[Brief description of the drawings]
FIGS. 1A and 1B show a part of a method for producing a compound semiconductor single crystal of the present invention, in which FIG. 1A is a schematic diagram showing a temperature distribution after melting a raw material and completing seeding, and FIG. After completion of the seeding, the temperature in the furnace is lowered while maintaining the temperature gradient to grow a single crystal from the seed crystal part, so that the average temperature of the raw material melt becomes lower than a temperature higher by 5 ° C. than the melting point. FIG. 6 is a schematic diagram showing a temperature distribution when the temperature of the furnace is stopped when the temperature in the furnace is lowered.
FIG. 2 is a schematic view of an apparatus for manufacturing a compound semiconductor crystal by a VB method according to Example 1 of the present invention.
FIG. 3 is a schematic view of an apparatus for manufacturing a compound semiconductor crystal by a VB method according to a second embodiment of the present invention.
FIG. 4 is a schematic diagram showing that the solid-liquid interface shape is concave on the melt side.
FIG. 5 is a schematic diagram showing that the solid-liquid interface shape is convex toward the melt side.
3 PBN crucible (crystal growth vessel)
3a Seed crystal part 3b Cross-sectional area increasing part (diameter increasing part)
3c Growth crystal part (straight body part)
4 GaAs polycrystalline raw material 5 Boron trioxide (liquid sealant)
6 seed crystal 7 crystal cradle 8 upper heater 9 middle heater 10 lower heater 11 top heater

Claims (3)

Using a container having a seed crystal part having a small cross-sectional area, a cross-sectional area increasing part having a gradually increasing cross-sectional area, and a growth crystal part having a large and substantially constant cross-sectional area following the seed crystal part, the raw material is added to the container. The melt is accommodated, and crystal growth is started from a seed crystal previously arranged at the bottom of the vessel in a growth furnace provided with a temperature gradient, and crystallization is gradually advanced upward. In the method for producing a compound semiconductor single crystal for crystallizing
After melting the polycrystalline raw material and completing the seeding, by lowering the furnace temperature, a single crystal is grown from the seed crystal part after the seeding is completed to a point where the cross-sectional area increases,
Next, a method for producing a compound semiconductor single crystal, characterized in that the decrease in the furnace temperature is stopped and the single crystal is grown by moving the vessel relative to the growth furnace. Using a container having a seed crystal part having a small cross-sectional area, a cross-sectional area increasing part having a gradually increasing cross-sectional area, and a growth crystal part having a large and substantially constant cross-sectional area following the seed crystal part, the raw material is added to the container. The melt is accommodated, and crystal growth is started from a seed crystal previously arranged at the bottom of the vessel in a growth furnace provided with a temperature gradient, and crystallization is gradually advanced upward. In the method for producing a compound semiconductor single crystal for crystallizing
After the polycrystalline raw material is melted and seeding is completed, the temperature in the furnace is lowered to allow a single point from the seed crystal part after completion of seeding to a certain point equal to or less than 1/4 of the entire length in the longitudinal direction of the grown crystal part. Grow crystals,
Next, a method for producing a compound semiconductor single crystal, characterized in that the decrease in the furnace temperature is stopped and the single crystal is grown by moving the vessel relative to the growth furnace. The method for producing a compound semiconductor single crystal according to claim 1 or 2,
After melting the polycrystalline raw material and completing the seeding, the temperature in the furnace is lowered to grow a single crystal from the seed crystal portion after the completion of the seeding, and the raw material melt at the time when the decrease in the furnace temperature is stopped. A method for producing a compound semiconductor single crystal, wherein the average temperature is lower than a temperature higher by 5 ° C. than a melting point.

Images